1. Technical Field
The present invention relates to a stackless continuous dual-sided copying method for photocopying machines.
2. Description of Related Art
Among photocopying machines, some are equipped with a continuous dual-sided copying function wherein dual-sided copying is carried out in a circulating conveyance path without stacking the copy sheets following one-sided copying (hereinafter referred to as a stack-less continuous dual-sided copying function). When carrying out continuous dual-sided copying in such photocopiers, copy sheets are fed successively, and reverse-side copying is performed successively on the fed copy sheets. A predetermined position on the circulating conveyance path (hereinafter called the circulatable sheet-count discriminating position) is for discriminating that the number of copy sheets being conveyed has reached a maximum value. The count of copy sheets that can stay in the circulating conveyance path defines this maximum value (hereinafter called the circulatable sheet count). When the sheet on which reverse-side copying was performed first reaches the circulatable sheet-count discriminating position, the copier discriminates that the count of copy sheets in conveyance is the circulatable sheet count, and halts fresh copy-sheet supply.
Thereafter, front-side copying is carried out successively on the copy sheets on which reverse-side copies were made. Then, once the front-side copying operation is performed for the last copy sheet currently being conveyed on the circulating conveyance path, sheet feeding is restarted and the same operations are repeated.
The circulatable sheet count differs according to, for example, copy size, copy mode and sheet-feed level, and therefore the circulatable sheet-count discriminating position also varies according to the copy size, copy mode and sheet-feed level. Therefore, copy-sheet detection sensors are disposed in a plurality of circulatable sheet-count discriminating positions determined beforehand in the circulatable conveyance path. The copy-sheet detection sensors are disposed at circulatable sheet-count discriminating positions determined based upon, in the present instance for example, copy size, copy mode and sheet-feed level. Based on the output from the copy-sheet detection sensors, whether or not the copy sheet on which reverse-side copying was first performed has reached the circulatable sheet-count discriminating position is discriminated.
A problem conventionally has been that discriminating whether the sheet count of copy paper being conveyed on the circulating conveyance path has reached the circulatable sheet count has necessitated utilizing a plurality of copy sheet detection sensors.
Conventionally too, when sheet feeding is resumed, shifting to the next continuous dual-sided copying cycle, copy sheets are fed from a sheet-feeding cassette and conveyed into the circulating conveyance path. The sheet-feeding cassettes are at multiple levels from the copy-sheet conveyance entry position. When sheet-feeding from a cassette that is in a location remote from the conveyance entry position, proceeding from resumption of the sheet-feeding operation to the point at which a copy sheet is conveyed to the registration roller pair takes time. This is a problem in that it lengthens the time it takes for continuous dual-sided copying operations.